1. Field of the Invention
The present invention relates to the field of metallurgical refining lances. More particularly, this invention relates to a nozzle of a refining lance for supplying post-combustion oxygen to the space above a molten metal bath undergoing refining.
Refining lances are known in the prior art which have, apart from vertical nozzles supplying supersonic refining oxygen, several auxiliary nozzles. These auxiliary nozzles have angles of between 25.degree. and 60.degree. (see, for example, patents LU 78 906 and LU 83 814) in relation to the vertical axis. They deliver jets of oxygen for the purpose of post-combustion. Because these jets of oxygen are subsonic, the auxiliary nozzles are fed by an independent oxygen circuit which permits adjustment of delivery.
A means of increasing the degree of turbulence of the jet is also known (see Patent LU No. 82 846) and is provided in the conduits of the nozzles which guide the post-combustion oxygen. Such turbulence increasing means may comprise plates arranged in the conduits of the secondary nozzles so as to form spirals. In another embodiment, the walls of the conduits are provided with grooves which may be circular and arranged in a plane perpendicular to the axis of the conduit or may be spiral. The angles of inclination of the post-combustion oxygen jets are dictated by those of the nozzles; once they have been determined by empirical tests or methods (taking into account the angles of the primary oxygen jets, their arrangement, the dimensions of the converter, the height of the head of the lance above the bath etc.), the angles remain constant. These prior art nozzles do not permit the space above the bath to be swept with jets of oxygen and they do not permit post-combustion oxygen to be sent to the converter at an angle which varies according to the refining stage in progress. Patent LU No. 86 329 (Corresponding to U.S. Pat. No. 4,730,814, which is assigned to the assignee hereof and fully incorporated herein by reference) describes a supersonic nozzle which supplies post-combustion oxygen at a variable angle to the space above a molten metal bath. This nozzle comprises a wall along which the gas passes in a straight line before ending at a pointed edge which forms part of the mouthpiece. The nozzle is level with the top of the pointed edge, and as a result, the jet expands and is deflected by the pointed edge. The angle of deflection varies according to the pressure of the gas at the edge, i.e. the higher the pressure of the gas is at this point, the greater the angle of deflection. Conversely, the deflection effect of the edge is practically nil when the gas has a subsonic speed at this point. By varying the pressure of the gas feeding the nozzle within predetermined limits, an angle close to 30.degree. can be swept. The resulting turbulences (from this pressure variance) in the converter favor the creation of an extended zone, permanently supplied with oxygen. Although this nozzle has a post-combustion rate superior to that of conventional nozzles, it may still be improved. Indeed, as a result of construction constraints (space available in the head of the lance) it is not possible to arrange these nozzles around the entire circumference of the head of the lance, but only in certain discrete places, so that the space is only fed in an imcomplete manner.